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SubjectRe: Possible regression due to "hrtimer: Get rid of hrtimer softirq"
On Thu, 7 May 2015, Simon Horman wrote:
> ------------[ cut here ]------------
> kernel BUG at kernel/irq_work.c:135!

BUG_ON(!irqs_disabled());

So something enables interrupts in the periodic tick handling
machinery. Seems you have high resolution timers disabled, but nohz
enabled. And that code path has a local_irq_disable/enable pair which
causes havoc. Patch below.

Thanks,

tglx

diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index 753c211f6195..812f7a3b9898 100644
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -967,11 +967,9 @@ static void tick_nohz_switch_to_nohz(void)
if (!tick_nohz_enabled)
return;

- local_irq_disable();
- if (tick_switch_to_oneshot(tick_nohz_handler)) {
- local_irq_enable();
+ if (tick_switch_to_oneshot(tick_nohz_handler))
return;
- }
+
tick_nohz_active = 1;
ts->nohz_mode = NOHZ_MODE_LOWRES;

@@ -986,7 +984,6 @@ static void tick_nohz_switch_to_nohz(void)
hrtimer_forward_now(&ts->sched_timer, tick_period);
hrtimer_set_expires(&ts->sched_timer, next);
tick_program_event(next, 1);
- local_irq_enable();
}

/*
@@ -1171,7 +1168,7 @@ void tick_oneshot_notify(void)
* Called cyclic from the hrtimer softirq (driven by the timer
* softirq) allow_nohz signals, that we can switch into low-res nohz
* mode, because high resolution timers are disabled (either compile
- * or runtime).
+ * or runtime). Called with interrupts disabled.
*/
int tick_check_oneshot_change(int allow_nohz)
{





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